To USB or Not to USB

UASP for Faster USB for Mass Storage

All USB Storage products, Flash Drives, Thumb Drives, Hard Drives, and SSDs use a transfer protocol called “Bulk Only Transfer” or “BOT” protocol. This works reliably in Windows and Linux and other operating systems.

In USB, a Bulk Transfers refers to a transfer of data that must be 100% accurate when it arrives. No errors can be allowed. For example, if you are copying pictures from your camera to your computer, you want every color pixel to be 100% accurate. The same is true for printing a picture.

It also means the data does not need to arrive at a certain time. If an error occurs in a Bulk transmission, the system retries until the data accurately moves to the destination.

BOT is highly reliable, but the hard drive companies knew that with USB 3.0 a new method would be needed. BOT basically sends a single packet at a time. This works well for USB 2.0.

USB 3.0 lets you send packets along multiple USB 3.0 “streams.” To take advantage of this, Storage companies created a new USB Driver Class, a purely software feature, to enable faster USB transfers on USB 3.0. called “USB Attached SCSI Protocol” or “UASP.” UASP allows you to send packets along multiple streams in parallel, and even burst the data faster.

Today, mass market hard drives today won’t deliver data fast enough because they use SATA 3 Gb/s instead of the faster 6Gb/s. Most hard drives bridge from SATA to USB 3.0. Since USB 3.0 has a maximum effective throughput of about 4Gb/s, this is faster than existing SATA 3/Gb/s drives. SATA can be limiting. Within 2 years, this will change because hard drives will have either SATA 6Gb/s support, or native USB 3.0 support so SATA will not be the bottleneck.

Eric started working on USB in 1995, starting with the world’s first BIOS that supported USB Keyboards and Mice while at Award Software. After a departure into embedded systems software for real-time operating systems, he returned to USB IP cores and software at inSilicon, one of the leading suppliers of USB IP. In 2002, inSilicon was acquired by Synopsys and he’s been here since. He also served as Chairman of the USB On-The-Go Working Group for the USB Implementers Forum from 2004-2006.

Eric received an M.B.A. from Santa Clara University and an M.S. in Engineering from University of California Irvine, and a B.S. in Engineering from the University of Minnesota. and is a licensed Professional Engineer in Civil Engineering in the State of California.